mutations, gene expression and cancer

Question 1

Explain what is meant by the terms totipotent and pluripotent.

Answer 1

• totipotent cells can give rise to a complete human/all cell types;
• pluripotent can only give some cell types;

Question 2

Explain how cells produced from stem cells can have the same genes yet be of different types.

Answer 2

• {not all / different} genes are switched {on / off} /active / activated ;
• correct and appropriate reference to factors /mechanisms for gene switching ;
• e.g. reference to promoters / transcription factors

Question 3

Describe the mechanism by which a signal protein causes the synthesis of mRNA.

Answer 3

• signal protein {binds to / joins to / interacts with / activates}
• receptor on surface membrane;
• messenger molecule moves from cytoplasm and enters nucleus;
• {produces / activates} transcription factor;
• binds to promoter region;
• RNA polymerase transcribes target gene;

Question 4

Explain how oestrogen enables RNA polymerase to transcribe its target gene.

Answer 4

• Oestrogen diffuses through the cell membrane;
• attaches to ERα receptor;
• ERα receptor changes shape;
• ERα receptor leaves protein complex which inhibited it’s action;
• oestrogen receptor binds to promoter region;
• enables RNA polymerase to transcribe target gene.

Question 5

What is RNA interference (RNAi)?

Answer 5

• two types of this RNA: microRNA (miRNA) and small interfering RNA (siRNA);
• single strand of miRNA/siRNA binds to a protein in the cytoplasm to form a complex;
• called a RNA-induced silencing complex (RISC);
• miRNA/siRNA has complementary base sequence to part of a mRNA molecule;
• RISC inhibits gene expression by binding to the complementary mRNA and either;
• the mRNA is hydrolysed by an enzyme;
• or inhibits the initiation of ribosomal translation;
• translation does not occur, polypeptide is not produced and expression of the gene has been silenced

Question 6

Compare the structure of dsRNA and DNA.

Answer 6

• Similarities; 2 max
• Polynucleotides/polymer of nucleotides;
• Contain Adenine, Guanine, Cytosine;
• Have pentose sugar/5 carbon sugar;
• Double stranded/hydrogen bonds/base pairs.
• Differences; 2 max
• dsRNA contains uracil, DNA contains thymine;
• dsRNA contains ribose DNA contains Deoxyribose;
• dsRNA is Shorter than DNA; fewer base pairs in length;

Question 7

Explain how the methylation of tumour suppressor genes can lead to cancer.

Answer 7

• Methylation prevents transcription of gene;
• Protein not produced that prevents cell division / causes cell death / apoptosis;
• No control of mitosis.

Question 8

Describe what is meant by a malignant tumour.

Answer 8

• mass of undifferentiated / unspecialised / totipotent cells;
• uncontrolled cell division;
• (not ‘repeated’)
• metastasis / (cells break off and) form new tumours /
• spread to other parts of body;

Question 9

Describe how altered DNA may lead to cancer.

Answer 9

• (DNA altered by) mutation;
• (mutation) changes base sequence;
• of gene controlling cell growth / oncogene / that monitors cell division;
• of tumour suppressor gene;
• change protein structure / non-functional protein / protein not formed;
• (tumour suppressor genes) produce proteins that inhibit cell division;
• mitosis;
• uncontrolled / rapid / abnormal (cell division);
• malignant tumour;

Question 10

Describe how alterations to tumour suppressor genes can lead to the development of tumours.

Answer 10

• (Increased) methylation (of tumour suppressor genes);
• Mutation (in tumour suppressor genes);
• Tumour suppressor genes are not transcribed / expressed OR Amino acid sequence / primary structure altered;
• (Results in) rapid/uncontrollable cell division;

Question 11

Define epigenetics.

Answer 11

• Heritable phenotype changes (gene function) that do not involve alterations in the DNA sequence/mutation.